In recent years, along with the proliferation of a low-priced high-performance video camera, there has been occurred such a case where a video image shown in a movie theater or the like is directly taken with a video camera in secret and copied on a DVD or the like, and the DVD having such an image copied thereon is illegally sold, and it has been an issue to ensure protection of copyright of a video image. As a method for dealing with such an issue, there has been proposed a digital watermark technology for a moving image signal (see, for example, Patent Document 1).
According to the conventional technology disclosed in Patent Document 1, a luminance variation pattern is embedded in a time direction and in a spatial direction as a digital watermark in a moving image to be protected by copyright. Further, a correlation value for a video signal of the video image to be subjected to detection, in relation to a detected pattern, is obtained, to thereby detect information embedded as the digital watermark. With the conventional technology, when copyright information is embedded as a digital watermark, it is possible to obtain the copyright information even from a recaptured image which is an illegal copy, and to claim the copyright thereto, which also serves as a deterrent against an illegal copy made by recapturing a video image.
Patent Document 1: JP 2006-517068 A (pp. 4 to 8 and FIG. 4)